1. Field of the Invention
The invention relates to a vehicle including a differential mechanism (such as a planetary gear mechanism) having at least three rotary elements between an internal combustion engine and drive wheels, and also relates to a control method for the vehicle.
2. Description of Related Art
In Japanese Patent Application Publication No. 2011-219025 (JP 2011-219025 A), a vehicle including a planetary gear mechanism (differential mechanism) between an engine and drive wheels is disclosed. The planetary gear mechanism includes a sun gear coupled, to a generator, a ring gear coupled to the drive wheels, a pinion gear that meshes with the sun gear and the ring gear, and a carrier coupled to the engine. In JP 2011-219025 A, a technology of preventing excessive rotation of the generator by restricting engine torque without departing from an acceleration request, when the acceleration request is made by the driver, in the vehicle as described above, is disclosed.
However, in the vehicle disclosed in JP 2011-219025 A, if power generated by the engine is controlled so as to prevent excessive rotation of the generator, without taking account of changes in rotational energy of the planetary gear mechanism, the excessive rotation may be promoted.
Namely, in a regular engine vehicle in which no planetary gear mechanism is provided between an engine and a transmission, a positive correlation constantly exists between power generated by the engine and the rotational speed of the engine. Namely, one of the engine power and the engine speed increases if the other increases, and one of the engine power and the engine speed decreases if the other decreases. Accordingly, it is possible to prevent excessive rotation by performing correction to reduce the power generated by the engine.
However, in a vehicle in which a planetary gear mechanism is provided between an engine and a transmission, like the vehicle disclosed in JP 2011-219025 A, the relationship between the power generated by the engine and the rotational speed of an input shaft of the transmission changes depending on conditions of the planetary gear mechanism, which may result in a negative correlation between the engine power and the input shaft speed of the transmission. Namely, one of the engine power and the input shaft speed increases if the other decreases, and one of the engine power and the input shaft speed decreases if the other increases. Therefore, in the vehicle disclosed in JP 2011-219025 A, if the correction is performed in the same manner as in the regular engine vehicle, the excessive rotation may be promoted depending on the conditions of the planetary gear mechanism.